Photosynthesis Flashcards
Word equation for photosynthesis
Carbon dioxide + water –> Glucose + oxygen
Chemical equation for photosynthesis
6CO2 + 6H2O –> C6H12O6 + 6O2
Pondweed photosynthesis experiment using CORMS
Change : Distance between lamp and beaker containing pondweed.
Organism: Elodea (pondweed)
Repeat: 10 x
Measure: Number of 02 bubbles produced in a minute at each distance. To improve experiment measure volume of 02 bubbles.
Same: Length of elodea, temperature, species of plant, type of light bulb, CO2 concentration
Control variables in pondweed experiment
Length of elodea used, temperature of beaker, species of plant, type of light bulb, CO2 concentration
Independent variable in pondweed experiment
Intensity of light/ distance between lamp and pondweed.
Dependant variable of pondweed experiment
Number of oxygen bubbles produced by pondweed in a minute or volume of oxygen bubbles produced by pondweed in a minute
Improvements to pondweed experiment
Keeping temperature controlled so rate of photosynthesis isn’t affected: Put the elodea in a boiling tube of water which is then placed in a beaker with a thermometer, to act as a water bath.
Accurate measurement of O2: Collect the gas (oxygen) produced in an inverted measuring cylinder to measure the volume of oxygen produced per time. Or use a gas syringe.
CO2 concentration: Add a fixed mass of sodium bicarbonate to water to provide a higher, constant concentration of CO2.
Steps for testing a leaf for starch.
Destarch the leaf for 24 hours in the dark before starting the experiment.
Place leaf in boiling water for 1 min.
Turn off the bunsen burner and transfer the leaf into a test tube containing ethanol and then place the test tube in hot water (acts as hot water bath)
Place the leaf in hot water to soften it.
Spread the leaf out on a white tile and cover it with Iodine solution.
Why is the leaf de-starched in the experiment?
So that the leaf is free from starch at the start of the experiment. Ensures any starch tested was made from glucose made in photosynthesis
How does placing the leaf in the dark destarch it?
Without any sunlight, photosynthesis doesn’t take place in the leaf. Photosynthesis produces glucose which is stored as starch in the leaf. Without photosynthesis, no glucose is produced and no starch is stored. The starch stores in the leaf are converted to glucose for respiration, to produced energy for the plant. The starch stores are used up.
Why is the leaf placed in boiling water at the start of the experiment?
To kill the tissue and break down the cell walls.
Why is the leaf boiled in ethanol?
To dissolve the chlorophyll so colour change can be seen more clearly.
Why is the leaf placed back in hot water/ rinsed with water?
To soften the leaf/ to allow Iodine to penetrate the leaf.
What colour does Iodine turn in presence of starch?
Yellow –> blue/black
How would you change the experiment if you wanted to show that a leaf needed light for photosynthesis?
Cover part of the leaf so it isn’t exposed to sunlight. Only the part of the leaf exposed to sunlight will produce starch and turn blue/black
How would you change the experiment if you wanted to show that chlorophyll is required for photosynthesis?
Use a variegated leaf. The white parts of leaf lack chlorophyll. Only the green parts of the leaf (containing chlorophyll) will produce starch. Green parts of leaf contain the green pigment chlorophyll which is used in photosynthesis.
How would you change the experiment if you wanted to show that carbon dioxide is needed for photosynthesis?
One leaf of a plant is enclosed in a conical flask (or
plastic bag) containing soda lime to absorb the carbon dioxide and this leaf is compared
to another enclosed in a flask but without the soda lime. Only the leaf that had access to
carbon dioxide (not soda lime one) produces starch.
Explain why the ‘Testing a leaf for starch’ experiment shows what is needed for photosynthesis.
Photosynthesis produces glucose, which is stored in the leaves as starch. When a leaf has photosynthesised, starch will be present.
Safety precautions for ‘testing a leaf for starch’ experiment.
Ethanol is flammable so turn off the bunsen burner when boiling the leaf in ethanol. Safest way to heat ethanol is in an electric water bath.
Iodine is an irritant to the eyes so wear goggles.
Describe how energy for photosynthesis reaction is gained by plants.
Light is absorbed by chloroplasts/ chlorophyll
Limiting factors of photosynthesis
Carbon dioxide, temperature and light intensity
Describe and explain the waxy cuticle
Protective layer, prevents water from evaporating
Describe and explain the upper epidermis
Thin and transparent to allow light to penetrate through to the palisade mesophyll layer
Describe and explain the palisade mesophyll
Long, thin cells tightly packed with lots of chloroplasts to absorb more light, maximising photosynthesis
Describe and explain the spongy mesophyll
Contains air spaces that increase surface area to volume ratio for the diffusion of gases
Describe the lower epidermis
Contains guard cells and stomata
Describe and explain the guard cell
Opens and closes the stomata to allow CO2 to diffuse in and oxygen to diffuse out
Describe and explain the stomata
Where gas exchange takes place. Evaporation of water also takes place here.
Describe and explain the vascular bundle
Contains xylem and phloem to transport substances to and from the leaf
Describe and explain the xylem in the leaf
Transports water into leaf for mesophyll cells to use in photosynthesis and for transpiration from stomata
Adaptations of root hair cell
High surface area for maximum water and mineral absorption
Lots of mitochondria so lots of energy produced for active transport of minerals
No chloroplasts, no photosynthesis
Why do stomata open in the light?
In light, guard cells photosynthesise, sugar concentration increases (glucose produced) so water potential decreases. Water moves into the guard cells by osmosis so they become turgid. Because of the inflexible inner cell wall the guard cells change shape, opening the stomata.
Why do stomata close in the dark?
Photosynthesis doesn’t occur in the dark. Sugar concentration falls (due to respiration), water potential increases and water moves out of the guard cells. This causes the guard cells to become flaccid and the stomata close.
What are the 3 main minerals plants need?
Nitrates, magnesium ions and phosphates
What are nitrates used for in plants?
Used to create amino acids and proteins, needed for cell growth
What are magnesium ions used for in plants?
Used to make chlorophyll which is needed for photosynthesis
What are phosphates used for in plants?
Used to make nucleic acids (RNA and DNA) and cell membranes
Observation of a plant with a nitrate deficiency
Stunted growth
Observation of a plant with a magnesium deficiency
Yellow leaves
Observation of a plant with a phosphate deficiency
Poor root growth, purple leaves
How is the leaf adapted for photosynthesis?
Thin so short diffusion distance
Leaf is wide for large surface area for diffusion
Upper epidermis transparent to allow light through
Palisade mesophyll cells contain many chloroplasts to absorb light
Spongy mesophyll have air spaces for gas exchange/diffusion
Stomata absorbs carbon dioxide
Xylem/vascular bundle brings water for photosynthesis
